Evidence of multiple spawning in wild amphidromous type ayu.

This article presents a study on the occurrence of multiple spawning in the wild amphidromous type ayu. Adult ayu were collected from the Nezugaseki River in Yamagata, Japan by cast net or by electrofishing during autumn of 2001. The collected fish were killed with tricaine methanesulfonate and sectioned. Female ayu were divided into three groups by the occurrence of post ovulatory follicles. The results demonstrate the occurrence of multiple spawning in wild amphidromous type ayu, and also indicate that multiple spawning is a common phenomenon in the Nezugaseki River.